EP0786411A2

EP0786411A2 - A composite container

Info

Publication number: EP0786411A2
Application number: EP97850006A
Authority: EP
Inventors: Yngve Holmberg
Original assignee: Akerlund and Rausing AB
Current assignee: TRITELLO AB
Priority date: 1996-01-24
Filing date: 1997-01-17
Publication date: 1997-07-30
Also published as: NO970297D0; NO970297L; EP0786411A3; DE29601117U1

Abstract

A composite container and a method for manufacturing of such a container, where the shrinkage between an outer member and an inner liner is dealt with by providing the container bottom with at least one, in situ made, embossed elevated bottom panel region during thermoforming of the inner liner into the outer member.

Description

TECHNICAL FIELD:

The present invention relates to composite containers, more precisely to containers comprising an outer tray-shaped member and an inner lining. Such containers can be manufactured of different materials for the members. However, one of said members should have the capacity of providing sufficient strength for the overall container structure and, additionally, the outer member must be of a type where high quality printing is possible by use of efficient printing machinery.
Cardboard material has the necessary strength and such material can be printed in high speed operations, in sheet form or roll form, and cardboard is a relatively cost-efficient material. There are well-developed techniques for coating cardboard with thermo-plastic material in order to provide heat-sealing capability, which provides a cost-effective method of obtaining adherence of an inner product-contacting lining of a composite container.

BACKGROUND OF THE INVENTION:

For years the quality and the production efficiency of composite containers of the present type have been upgraded and the present equipment and facilities for production are of a very high efficiency. The material forming the outer member of the composite container, in this case cardboard material, is supplied in roll form, pre-coated or not pre-coated with thermoplastic material, to the plant of the package manufacturer. In roll form or in sheet form, the cardboard material is processed in several high-speed production lines, including printing, surface coating in separate steps or a multi-coating process and punching the processed material into individual blanks for outer members of the composite containers.
The surface of that side of the blank which is to face the interior and to which a lining should be attached, is provided with an adequate surface coating suitable for the actual type of material of the lining. One efficient surface coating is thermoplastic materials of the so-called hot melt type.
For the overall strength of the composite container it is essential that there is an attachment or adherence of high strength between the two container members.
In a production machinery of high production rate such attachment or adherence is obtained by feeding a thermoplastic material in roll form as an integral web over an array of moulds where in each one of such moulds an individual outer member blank, in the present case of cardboard or similar material, has been inserted and erected. Additionally, the side walls of the erected blank have been attached to each other for forming a stable "shell" for thermoforming the web-type thermoplastic material into each one of the moulds.
The thermoforming is done by means of heat and pressure, normally by means of a plunger and vacuum, and the heat energy of the process will also activate the thermoplastic material of the facing side of the outer member. After the pressure has been relieved and the temperature lowered, there will be a heat seal between the two facing surfaces of the outer and inner members.
For providing maximum strength, heat sealing over the entire surface area is to be preferred.
Thermoplastic materials have a shrinkage tendency after the forming process when built-in tensions of the thermoplastic material are relieved. When increasing the product-containing volume of the composite container such shrinkage will be more noticeable. Especially the bottom panel of the container has a tendency to bulge outwards when the inner lining shrinks. Such an outwardly-bulged bottom presents problems in the handling at the product filler plant and is of course not attractive from a consumer point of view.
In order to cope with such problems prior art techniques already suggest that an embossment, facing in an inward direction of the composite container to be manufactured, is pre-embossed in the cardboard material during the normal converting procedure, i.e. when punching individual blanks out of the cardboard material.
However, during such punching the embossment possibilities are very restricted because of the combined operation of punching and embossing. There is available only a very limited elevation of the embossed region. The embossing is, of course, not allowed to tear the cardboard material, which is of limited strength, and the provision of embossing tools providing different heights or elevations of embossed regions is not possible without negatively affecting the punching operation and the overall look and quality of the cardboard material.

SUMMARY OF THE INVENTION:

The object of the invention, therefore, is to provide a composite container where differences in shrinkage characteristics of the inner and outer member have been dealt with.
The invention provides a composite container, comprising an outer cardboard tray, an inner thermoformed lining and means for providing surface adherence between the tray and the lining, said cardboard tray being formed from a blank comprising a bottom panel, side wall panels and end flaps to be joined to the side wall panels when erecting the blank, and said bottom panel being provided with an embossment defining an elevated first bottom panel region extending over a major part of the bottom and extending in a direction inwards of the erected tray. The composite container is characterized by at least one further embossment in said elevated bottom panel region defining a still further elevated second bottom panel region.
In a preferred embodiment said elevated first bottom panel region joins a circumferential unembossed bottom region of uniform width between said embossment and the margin of the bottom panel.
In this embodiment said still further elevated second bottom panel region is placed centrally within said first embossment.
Preferably, said first and second embossments are defined by uniform contour lines.
In one further embodiment a third embossment, for instance of circular contour, is placed within said second embossment region.
The invention also provides a method of manufacturing a composite container, comprising an outer cardboard tray, an inner thermoformed lining and means for providing surface adherence between the tray and the lining, where the cardboard tray blank comprising a bottom panel, side wall panels and end flaps is erected in a mould and the end flaps are attached to the side walls, a web or sheet of thermoplastic material is formed down into the erected blank and the means for providing surface adherence is activated.
The method is characterized in that during the forming operation at least one embossment defining an elevated bottom panel region is made in the bottom panel of the blank.
Said embossment is made by use of a male type of protruding region in the mould bottom, and by using the forming pressure, for instance from a plunger.
In one embodiment said embossment is made within a pre-made embossment of the bottom panel of the blank.
In one embodiment the pre-made embossment joins a circumferential unembossed bottom region of uniform width between said pre-made embossment and the margin of the bottom panel.
Preferably, the embossment made during the forming operation is made with an outer contour essentially uniform to the pre-made embossment.
In still a further embodiment a further embossment is made within the contour of the embossment made during the forming operation.

A PREFERRED EMBODIMENT:

One embodiment of the present invention will now be described with reference to the accompanying drawings, where:

Figure 1: is a schematic overall view of a production machinery for composite containers of the present type,
Figure 2: represents a view of a cardboard blank for the outer tray,
Figure 3: schematically shows the blank placed in a mould,
Figure 4: is a view showing the composite container after the lining has been formed,
Figure 5: is a view similar to the one in Figure 4, in enlarged scale showing the portion of the composite container enclosed within broken lines in Figure 4, and
Figure 6: is a view similar to the one in Figure 5 but showing a composite container without the further embossments according to the present invention.

In Fig. 1, the reference numeral 10 represents a stand where a roll 11 of thermoformable plastic material is supported, fed and guided to a thermoforming station 15. The thermoformable web 12 is passed through a pre-heating station 16 and arrives at the forming station 15 where plungers and/or vacuum and pressure facilities (not shown) are used for the forming operation.
Mould arrays 13, 17 are supported in the stand 10 and moveable to and from the forming station crosswise the feeding direction of the thermoplastic web 12.
In the mould array 13, in each one of the moulds, an individual outer tray cardboard blank is inserted by an insertion mechanism (not shown) and the complete mould array is placed under the web 12 in the forming station 15 where the web is pushed down into the individual moulds. The array of moulds with composite containers is thereafter transported further crosswise the web feeding direction into an unloading station 18.
In Fig. 2, an individual blank of cardboard material for forming the outer member or tray of the composite container is shown. The blank comprises a bottom panel 19 with a central embossment 20 therein facing in a direction corresponding to a direction inwards of the tray to be erected. Around the central embossment 20 there is a circumferential unembossed remaining strip 20' of material. Integral with the bottom panel 20 there are side wall panels 21, 22 and end flaps 23, 24. All of the panels and flaps are coated with a thermoplastic material, for instance of hot melt type, on the appropriate surface thereof, i.e. the one which will be facing the lining of thermoplastic material to be attached to the cardboard blank.
In Fig. 3, there is shown schematically a mould 25 and the blank 19 inserted therein. The mould bottom is provided with three ledges or embossment/ support protrusions 26, 27, 28. The ledge 28 supports the pre-embossed bottom panel region 20 at the outer margin thereof. The radially outer contour of the ledge 28 corresponds to the contour line between regions 20 and 20'. The ledge 26, having the same outer contour as ledge 28, is placed at an elevated level in the mould bottom. The function of the ledge 26 is to emboss the bottom panel and form the elevated bottom panel region 29 of the composite container shown in Fig. 5. As appears from said figure, the pre-embossed region 20, after the forming in the mould 25, will be somewhat depressed, but will still not fall under the line 33 shown in broken lines and which represents the plane which is critical for a proper support of the container, i.e. without any problems with an outwardly bulging bottom.
The elevated central embossing portion 27 of the mould bottom provides another, more elevated bottom panel region 30 than the elevated region 29 and further removes the entire bottom structure of the composite container in the proper direction from the critical support plane 33.
By comparison, Fig. 6 indicates what would happen without the elevated bottom panel regions 29, 30. Clearly, there is no planar support like the one shown by reference numeral 33 in Fig. 5.
Of course, the embodiment described is just a preferred embodiment and there is a great variety of embossment possibilities within the scope of the enclosed claims. The definition "cardboard material" of course includes other equivalent materials and within the definition of thermoplastic and thermoformable materials there is of course included laminates as well as mono-layer material compositions.

Claims

A composite container comprising an outer cardboard tray (31), an inner thermoformed lining (32) and means for providing a surface adherence between the tray and the lining, said cardboard tray being formed from a blank comprising a bottom panel (19), side wall panels (21, 22) and end flaps (23, 24), and said bottom panel being provided with an embossment (20) defining an elevated first bottom panel region extending over a part of the bottom and in a direction inwards of the erected tray,
characterized by at least one further embossment (29) in said elevated bottom panel region defining a still further elevated second bottom panel region.
A composite container as in claim 1, where said elevated first bottom panel region (20) joins a circumferential unembossed bottom region (20') of uniform width between said embossment and the margin of the bottom panel, characterized in that said still further elevated second bottom panel region is placed centrally within said first embossment.
Composite container as in claim 2, characterized in that said first and second embossments are defined by uniform contour lines.
A composite container as in claim 2, characterized in that a third embossment (30) is placed within said second embossment region.
A method of manufacturing a composite container, comprising an outer cardboard tray, an inner thermoformed lining and means for providing adherence between the tray and the lining, where a cardboard blank comprising a bottom panel, side wall panels and end flaps is erected in a mould and the end flaps are attached to the side walls, a web or sheet of thermoplastic material is formed down into the erected blank and the means for providing surface adherence is activated, characterized in that during the forming operation at least one embossment defining an elevated bottom panel region is made in the bottom panel of the blank.
A method as in claim 5, characterized in that said embossment is made by use of a male type of protruding region in the mould bottom, and by using the forming pressure, for instance from a plunger.
A method as in claim 6, where the pre-made embossment joins a circumferential unembossed bottom portion of uniform width between said pre-made embossment and the margin of the bottom panel, characterized in that the embossment made during the forming operation is made with an outer contour essentially uniform to the pre-made embossment.
A method as in claim 7, characterized in that a further embossment is made within the contour of the embossment made during the forming operation.